The present invention is directed to apparatus and methods of sample purification, and more particularly, to apparatus and methods of high throughput purification of samples from a chemical library.
The relationship between structure and functions of molecules is a fundamental issue in the study of biological and other chemistry-based systems. Structure-function relationships are important in understanding, for example, the function of enzymes, cellular communication, cellular control and feedback mechanisms. Certain macromolecules are known to interact and bind to other molecules having a specific 3-dimensional spatial and electronic distribution. Any macromolecule having such specificity can be considered a receptor, whether the macromolecule is an enzyme, a protein, a glycoprotein, and antibody, or an oglionucleotide sequence of DNA, RNA, or the like. The various molecules which bind to receptors are known as ligands.
A common way to generate ligands is to synthesize molecules in a stepwise fashion in a liquid phase or on solid phase resins. Since the introduction of liquid phase and solid phase synthesis methods for peptides, oglionucleotides, and small organic molecules, new methods of employing liquid or solid phase strategies have been developed that are capable of generating thousands, and in some cases even millions of individual compounds using automated or manual techniques. A collection of compounds is generally referred to as a chemical library. In the pharmaceutical industry, chemical libraries of compounds are typically formatted into 96-well microtiter plates. This 96-well formatting has essentially become a standard and it allows for convenient methods for screening these compounds to identify novel ligands for biological receptors.
Recently developed synthesis techniques are capable of generating large chemical libraries in a relatively short period of time as compared to previous synthesis techniques. As an example, automated synthesis techniques for sample generation allows for the generation of up to 4,000 compounds per week. The samples, which contain the compounds, however, typically include 20%-60% impurities in addition to the desired compound. When samples having these impurities are screened against selected targets, such as a novel ligand or biological receptors, the impurities can produce erroneous screening results. As a result, samples that receive a positive result from initial screening must be further analyzed and screened to verify the accuracy of the initial screening result. This verification process requires that additional samples be available. The verification process also increases the cost and time required to accurately verify that the targeted compound has been located.
Samples can be purified in an effort to achieve an 85% purity or better. Screening of the purified samples provides more accurate and meaningful biological results. Conventional purification techniques, however, are very slow and expensive. As an example, conventional purification techniques using high-pressure liquid chromatography (HPLC) take approximately 30 minutes to purify each sample. Therefore, purification of the 4,000 samples generated in one week would take at least 2000 hours (i.e. 83.3 days or 2.77 months).
Conventional purification techniques, such as HPLC, also require large volumes of solvents and result in large volumes of waste solvent. Disposal of the solvents, particularly halogenated solvents, must be carefully controlled for legal and environmental reasons, so the disposal process can be laborious and very costly. Disposal of non-halogenated solvents is less rigorous. Accordingly, when halogenated and non-halogenated solvents are used, the waste solvents are separated. The separation process of large volumes of solvents, however, can be a difficult process to perform efficiently and inexpensively. Accordingly, purification of large chemical libraries can be economically prohibitive. Therefore, there is a need for a faster and more economical manner of purifying samples of large chemical libraries.
Supercritical fluid chromatography (SFC) provides faster purification techniques than HPLC. SFC utilizes a multiphase flow stream that includes a gas, such as carbon dioxide, in a supercritical state, a carrier solvent and a selected sample. The flow stream passes through a chromatography column, and is then analyzed in an effort to locate target compounds. SFC is beneficial because the solvent and sample are carried by the gas and the amount of solvent needed during a purification run is substantially less than the volume used in HPLC. Also, the amount of waste solvent at the end of a run is substantially less, so less waste solvent needs to be handled. SFC, however, requires pressure and temperature regulation that is difficult to control accurately and reliably long term.
There are many different configurations of the purification instruments. They typically share commonality in the concept wherein that samples are delivered to a chromatography instrument where compounds are separated in time, and a fraction collector collects the target compound. In order for these instruments to maintain the high throughput process, the instruments must be able to handle large sample numbers, as well as large samples in terms of mass weight and solvent volume. Tradition would specify the use of a semiprep or prep scale chromatography system for a typical milligram synthesis. While this is achievable, it has a low feasibility in a high throughput environment because several issues become apparent in such practice: large solvent usage, generation of large amounts of solvent waste, expensive large-bore columns, and relatively large collection volumes of target compounds. If the proper flow rate or column size is not used, sufficient chromatographic purity will not be achieved.
Further drawbacks experienced with high throughput purification techniques include durability of components to accommodate the high pressures, high volumes, or high flow rates of samples through the purification system. The purification system requires extreme accuracy and very high tolerances to avoid cross-contamination and to ensure purified compounds. The system components, thus, must be sufficiently durable to accept the aggressive environment while still providing the accurate results required. If the components are not sufficiently durable and they break or require repair too quickly, the purification system must be taken out of service to replace or repair the components.
A further drawback experienced in conventional purification processes of large chemical libraries includes sample management during the purification process. As an example, the chemical libraries are typically maintained in sets of 96-well microtiter plates, wherein each well includes a separate sample. Each sample is carefully tracked by its xe2x80x9cwell addressxe2x80x9d within the microtiter plate. When a sample or portion of a sample is removed for purification from a selected well of a microtiter plate, the purified sample is typically collected in a separate container, processed, and eventually returned to a receiving well in a similar microtiter plate. That receiving well preferably has a corresponding well address in the microtiter plate so as to maintain the accuracy of the library records regarding sample location in the respective microtiter plate.
Conventional purification processes typically require the reformatting of a purified sample because the large collected volumes of fluid (e.g. the solvent that contains the purified sample) is greater than the volume of a receiving well in a conventional microtiter plate The large collected volumes must be reduced to a volume that fits into the microtiter plate""s well. The reduced volume of fluid containing the purified sample is also tracked and deposited into the appropriate well of the receiving microtiter plate that correctly maps to the well location from which the sample was taken at the start of the purification run. Such reformatting of purified samples into the receiving microtiter plate increases the time requirements and cost of the purification processes. Therefore, there is a need for a purification process that allows for quick and economical purification of samples that result in purified samples being collected directly to microtiter plates mapped directly to the original plate.
The present invention is directed to apparatus and methods of multiple channel high throughput purification of samples from a chemical library that overcome drawbacks experienced in the prior art. In an illustrated embodiment of the present invention, the method of multiple channel high throughput purification simultaneously purifies a plurality of samples, such as four samples, from a chemical library.
The method of the illustrative embodiment includes simultaneously purifying by supercritical fluid chromatography (SFC) all four samples in four channels of a purification system. The method includes passing,a first sample along a SFC flow path of the first channel, separating the first sample into sample portions, spacing the sample portions apart from each other along at least a portion of the first fluid path. The pressure of the supercritical fluid in the flow stream is regulated with a backpressure regulator and a pressure relief valve. The method also includes moving the separated sample portions along the fluid path, and detecting at least one sample portion flowing along the fluid path. The method further includes diverting a sampling away from the sample portion, directing the sampling to an analyzer while the remainder of the sample portion continues along the fluid path, analyzing the sampling with the analyzer, and determining if the one sample portion has selected sample characteristics. The method also includes collecting the one sample portion in a first receptacle, such as a well of a first microtiter plate, only if the sample portion has the selected sample characteristics. If the sample portion does not have the selected sample characteristics, the sample portion is collected in a second receptacle, such as a corresponding well in a second microtiter plate.
The multiple channel high throughput purification method of this illustrated embodiment further includes purifying a second sample along a second channel substantially simultaneously with the purification of the first sample. Purifying the second sample includes passing the second sample along a second flow path of the second channel, separating the second sample into sample portions, and spacing the sample portions apart from each other along at least a portion of the second fluid path. The method also includes moving the separated sample portions along the second fluid path, and detecting at least one of the sample portions flowing along the second fluid path. The method includes regulating the second sample""s pressure along the flow path. The method further includes taking a sampling from the one sample portion and directing the sampling to the same analyzer used for the first channel. The remainder of the sample portion continues to flow along the second fluid path.
The method also includes analyzing the second sampling with the analyzer, wherein the first and second samplings are analyzed separately in accordance with a selected analysis priority protocol. The analysis of the second sampling determines if the sample portion has selected sample characteristics. The method further includes collecting the sample portion in a separate receptacle, such as a separate well in the first microtiter plate identified above, only if the sample portion has the second selected sample characteristics. If the sample portion does not have the selected sample characteristics, the sample portion is collected in another receptacle, such as a separate well in the second microtiter plate identified above.
In one embodiment of the invention, the method of high throughput purification includes purifying third and fourth samples along corresponding third and fourth channels in a manner similar to the purification discussed above regarding the first and second samples. In this embodiment, the same analyzer is used to analyze samplings from all four samples. The samplings are all analyzed separately and in accordance with the selected analysis priority protocol.
The invention is also directed to a multiple channel high throughput purification system for substantially simultaneously purifying a plurality of samples from a chemical library. In one illustrated embodiment, the system includes a controller and a sample analyzer coupled to the controller, wherein the analyzer is configured to determine whether the samplings have selected sample characteristics. First, second, third, and fourth purification channels are coupled to the sample analyzer. The first purification channel includes a separation device positioned to receive a sample flow and to separate a first sample into sample portions so the sample portions are spaced apart from each other in the sample flow. A detector is positioned to receive the sample flow from the separation device and to detect at least one sample portion within the first sample. An adjustable backpressure regulator receives the flow stream from the detector and controls the pressure of the flow stream within the first channel.
A microsampling device is positioned to receive the sample flow from the backpressure regulator and is movable between open and closed positions while allowing a substantially continuous flow stream to pass through the device. In the closed position, the microsampling device blocks the flow stream from passing to the analyzer and allows the flow stream continues to flow through the device. In the closed position, the microsampling device also allows a substantially continuous flow of carrier fluid to pass therethrough to the analyzer. In the open position, the microsampling device directs a sampling of at least the one sample portion to the analyzer for analysis, while a remainder of the one sample portion in the sample flow moves substantially uninterrupted through the microsampling device.
A pressure relief valve receives the remainder sample flow from the microsampling device and maintains a selected pressure in the sample flow downstream of the microsampling device. A flow directing valve is in fluid communication with the first flow path and is positioned to receive the sample flow downstream of the pressure relief valves. The flow directing valve is moveable to a first position to direct the one sample portion in one direction if the analyzer has determined that the one sample portion has the selected sample characteristics. The flow directing valve is movable to a second position to direct the one sample portion in another direction if the analyzer has determined that the one sample portion does not have the selected sample characteristics. A first receptacle, such as a well of a microtiter plate, is positioned to receive the one sample portion from the flow directing device when the flow directing device is in the first position because the sample portion has the selected characteristics. A second receptacle, such as a well in a second microtiter plate, is positioned to receive the one sample position when the flow directing device is in the second position because the sample portion does not have the selected characteristics.
The second purification channel of the purification system includes a separation device positioned to receive a second,sample flow and to separate a second sample into sample portions. A separate detector is coupled to the separation device and is positioned to receive the second sample from the separation device. The detector is configured to detect at least one of the sample portions within the sample flow. A microsampling device is positioned to receive the sample flow from the detector and is movable between open and closed positions. When the microsampling device is in the closed position, the microsampling device allows the second sample flow to pass therethrough while being blocked from passing to the analyzer. In the open position, the microsampling device directs a sampling of the one sample portion to the analyzer for analysis, while the remainder of the sample portion continues along the second flow path substantially uninterrupted. A back pressure regulator and a pressure relief valve receive the second sample flow upstream and downstream, respectively; of the microsampling device to selectively control the pressure of the second sample flow along the second purification channel. A flow directing valve is in fluid communication with the second flow path and is positioned to receive the sample flow therethrough. The flow directing valve is moveable to a first position to direct the one sample portion in one direction if the analyzer has determined the sample portion has the selected sample characteristic. The flow directing valve is moveable to a second position to direct the one sample portion in another direction if the analyzer has determined that the sample portion does not have the selected sample characteristics.
A receptacle, such as a separate well in the first microtiter plate, is positioned to receive the sample portion from the flow directing device when the flow directing device is in the first position because the sample portion has the selected characteristics. Another receptacle, such as a separate well in the second microtiter plate, is positioned to receive the sample portion when the flow directing device is in the second position because the sample portion does not have the selected characteristics.
In one embodiment of the invention, the purification system includes third and fourth purification channels that purify third and fourth samples substantially simultaneous with the purification of the first and second samples. Each of the third and fourth purification channels are coupled to the same analyzer and direct the sample portions to receptacles, such as wells in the first and second microtiter plates, discussed above.
An aspect of the invention provides a microsample or flow splitter valve for use in the high throughput purification system for purifying a selected sample from a chemical library. The purification system has a sample flow path, a carrier fluid flow path, and a sample analyzer in fluid communication with the sample and carrier flow paths. The microsample valve includes a valve body having an interior chamber therein, and sample flow inlet and outlet ports in fluid communication with the sample flow path and with the interior chamber. The valve body has a carrier fluid flow port in fluid communication with the carrier fluid flow path, and an outflow port channel in fluid communication with the analyzer. A stem is slidably disposed in the interior chamber and is moveable between first and second positions within the chamber. The stem has a fluid bypass channel that communicates with the sample inlet port and the outflow port when in the first position to allow a selected portion of the sample to flow to the analyzer. The stem blocks the carrier flow port when in the first position to prevent fluid from the carrier fluid flow path from moving into the outflow port.
The fluid bypass channel in the stem communicates with the carrier flow port and with the outflow port when in the second position to allow selected carrier fluid to flow through the valve body to the analyzer. The stem blocks the sample flow inlet port from communicating with the outflow port when in the second position to prevent the sample flow from flowing to the outflow channel.
An aspect of the invention also includes an automated fraction collection assembly that retains the microtiter plates in a fixed position and dispenses the sample portions into the selected wells in the micrtiter plates. The fraction collection assembly includes a dispensing needle through which the sample portion is dispensed into disposable expansion chambers and then into the microtiter plate. The dispensing needle is mounted on a dispensing head adapted to extend into a disposable expansion chamber into which the sample portion is condensed and then dispensed into the microtiter plate.
The dispensing head is movable from a pick-up position, where the expansion chambers are picked up, to a collection position over the microtiter plates, where the sample portions are dispensed into the selected well of the microtiter plate. The dispensing head is also movable from the dispensing position to a chamber drop-off position, where the expansion chambers are released into a waste receptacle, so the dispensing needles are exposed. The dispensing head is further movable to a wash position at a wash station on the fraction collection assembly, where the dispensing needles are washed to avoid cross-contamination between samples.